It is proposed to continue work on the extracellular proteolytic enzymes elaborated by bacteria resident in the human oral cavity and alimentary tract. One such enzyme, IgA protease, has a highly restricted substrate specificity which is limited to human IgA proteins of the IgA1 subclass. We are now planning to 1) continue work in purifying this enzyme from culture supernatants of Streptococcus sanguis 2) establish an assay system for the enzyme based on IgA as substrate 3) continue a search for low molecular weight peptide substrates to be used in assay procedures and 4) continue work on the biologic significance of this enzyme specificity for the overall function of the immune system using well defined human antibodies of the IgA class.